In situ forming implants (“ISIs”) have been investigated primarily for injection into soft tissue for sustained drug delivery (Hatefi A, Amsden B. Biodegradable injectable in situ forming drug delivery systems. Journal of Controlled Release 2002; 80(1-3):9-28). These systems were conceived due to the phase separation observed when a hydrophobic polymer dissolved in a water-miscible organic solvent is introduced to an aqueous environment, resulting in solidification of the polymer matrix (Shah N H, Railkar A S, Chen F C, Tarantino R, Kumar S, Murjani M, Palmer D, Infeld M H, Malick A W. A biodegradable injectable implant for delivering micro and macromolecules using poly(lactic-co-glycolic) acid (PLGA) copolymers. Journal of Controlled Release 1993; 27(2):139-147), By mixing drugs into the polymer phase prior to injection, a drug-loaded, solid depot can form upon injection into the body. Such systems are available in FDA-approved formulations, such as ATRIDOX®, for delivery of doxycycline into gum tissue, and ATRIGEL®, which is approved for delivery of leuprolide acetate for treatment of prostate cancer. These systems provide prolonged drug release, with an initial burst dependent on drug and solvent properties and a release period dependent on drug and polymer properties (Parent M, Nouvel C, Koerber M, Sapin A, Maincent P, Boudier A. PLGA in situ implants formed by phase inversion: Critical physicochemical parameters to modulate drug release. Journal of Controlled Release 2013; 172(1):292-304). As such, these injectable systems avoid the additional trauma that would be needed for implantation of large, solid dosage forms. Furthermore, the polymers are hydrolytically degradable, so there is no secondary surgery required to remove an implant after drug delivery is complete (Kenley R A, Lee M O, Mahoney T R, Sanders L M, Poly(lactide-co-glycolide) decomposition kinetics in vivo and in vitro. Macromolecules 1987; 20(10):2398-2403). Because these polymer systems are locally injectable and space-filling, they should be able to infiltrate and conform to complex geometries, such as a network of trabecular bone. However, these materials offer little in the way of structural support. The present invention provides an injectable system for recovering bone or periodontal tissue that provides for sustained drug delivery with structural support.